Characterization of a melatonin binding site in Siberian hamster brown adipose tissue.
Melatonin has been shown, in various rodent species, to mediate photoperiodic effects on body weight and, consequently, fat mass. Pharmacological investigations indicated that the brown adipose tissue of Siberian hamsters possesses a melatonin binding site with a dissociation constant of 570+/-300 pM and a density of 3.2+/-1.8 fmol/mg protein. This binding site can also be detected on mature brown adipocyte membranes. The rank order of potency of a variety of drugs to displace 2-[125I]iodomelatonin from binding sites on Siberian hamster brown adipose tissue was as follows: 2-iodomelatonin > melatonin = prazosin > GR135531 (5-methoxycarbonylamino-N-acetyltryptamine) > N-acetylserotonin > 6-chloromelatonin > S20304 (N-(2-(1-naphthyl)ethyl)cyclobutanecarboxamide) >> methoxamine, phenylephrine, serotonin. Mel(1a) mRNA was not detected by RT-PCR (reverse transcription-polymerase chain reaction) in brown adipose tissue. Melatonin had no effect on either basal or stimulated lipolysis. Moreover, melatonin did not modify intracellular cAMP accumulation or inositol phosphate content. Together, these results suggest that the melatonin binding site characterized in brown adipose tissue is clearly different from the Mel(1) cloned subtype and has some features different from those of the Mel2 subtype.
Le Gouic
S
S
CNRS UPRESA 5018, UPS, IFR Louis Bugnard, Toulouse, France.
Atgié
C
C
Viguerie-Bascands
N
N
Hanoun
N
N
Larrouy
D
D
Ambid
L
L
Raimbault
S
S
Ricquier
D
D
Delagrange
P
P
Guardiola-Lemaitre
B
B
Pénicaud
L
L
Casteilla
L
L
D002001:Adipose Tissue, Brown / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D007295:Inositol Phosphates / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000378:metabolism; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D017111:Phodopus; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000378:metabolism*; D044094:Receptors, Melatonin
D000975:Antioxidants; D007295:Inositol Phosphates; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D000242:Cyclic AMP; D008550:Melatonin